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BUILDING A BETTER FUTURE WITH CHP


Nigel Thompson, Sales Manager – Gas Power Solutions at Finning UK & Ireland (Finning), a provider of both natural gas and biogas CHP technologies, advises on the factors to consider when specifying a CHP system and weighs up the benefits of using gas reciprocating engines over gas turbines.


uCG132‐16 Gas Generator. The recently introduced Cat CG range is designed for maximum efficiency in extended‐duty distributed generation and cogeneration applications including industrial and commercial facilities, utilities, wastewater treatment plants, landfill, mines, greenhouses and agriculture.


generation systems are considerable. Building services professionals and specifiers should be aware that a standard power-only generation system is typically only 40 per cent fuel-efficient, with all the potential thermal energy produced simply going to waste. By capturing useable heat with a CHP system, fuel efficiency can increase to more than 75 per cent, and in some cases as much as 88 per cent. A CHP system consists of a prime mover, such as an internal combustion engine or gas turbine to provide motive power, an electrical generator and a means of recovering heat. This is typically from the engine jacket cooling circuit via a plate heat exchanger and from the exhaust gas stream via a shell and tube heat exchanger. Alternatively, exhaust gases can be used to generate steam. As a result, a CHP solution reduces the amount of electricity the site purchases from the grid and the volume of fuel required to generate the appropriate amount of heat for the site.


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Not only does a CHP system harness the power of both electricity and heat in a single process, delivering improved efficiency and reduced energy costs, there are a number of other financial and environmental


he benefits of combined heat and power (CHP) applications over traditional electricity


incentives for specifiers. Generally a gas-fired product, a CHP system is cleaner than many other fossil fuels, typically delivering a 3:1 improvement of CO2 emissions into the


atmosphere. It also offers a range of tax incentives, such as enhanced capital allowances and certain business rate exemptions. Furthermore, the right CHP system can realise significant cost savings in the long-term compared to other capital investments in plant and equipment.


Specifying a CHP solution


Technical, financial and operational factors need to be considered when specifying a CHP system, as well as adhering to any required planning or building regulations. It is important to note that a CHP system makes savings when running, so there must be an on-going need for electricity and heat to justify the investment. It is generally


recommended that a site requiring heat and power together for more than 4,000 hours a year is suitable. Typical applications include the industrial, commercial and public sector, with buildings such as hospitals, universities, leisure centres, offices and retailers often opting for a CHP solution. An energy audit will determine whether a CHP system is a sound investment. The efficiency of the system will depend on a building’s base electrical load profile. A


site’s demand for electricity can vary drastically during the year, featuring a range of peaks and troughs, which is why electricity consumption should be calculated on the base level to ensure the CHP system can withstand the day-to-day demands placed on it.


A CHP solution that is too large for the application will not save money, which is why the system’s


configuration is so crucial. It is important to bear in mind that the cheapest CHP solution identified in the procurement process may not offer the best overall savings when it comes to total cost of ownership. For new buildings, specifiers can use predictive data based on designs or available benchmark data to determine the electricity usage from similar buildings. Utility suppliers will be able to provide half-hourly electricity data for existing buildings. In some instances, it can be more economic to oversize the CHP system to deliver more power that the base load requirement, with the option to sell any excess electricity generated back to the National Grid at a profit. In other applications, it can be more profitable to size it to the site’s lowest average heat demand, with the CHP system acting as the lead boiler and other back-up boilers supporting with any additional heat requirements. It is also advisable to purchase an operations and maintenance (O&M) contract at the same time as installation. Specifiers should seek a trusted partner with a strong track record of delivering CHP systems, who considers each site’s individual requirements. Finning not only offers expert advice and guidance on the specification and installation of a CHP unit, but also provides an O&M contract to help ensure efficiencies are delivered as promised.


Gas engines or gas turbines?


When installing a CHP system, specifiers can choose between two primary power sources: gas reciprocating engines or gas turbines. Each technology has attributes that will make it more suitable for the specific conditions of fuel type and quality, electric and heat load profile, physical space, altitude, ambient conditions and other factors.


Turbines are well suited for 30 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2016


uFeaturing a containerised Caterpillar G3512E gas engine with an electrical output of 1.0 MWe, the CHP solution supplied to Janssen Pharmaceuticals includes an exhaust gas boiler producing up to 625kg/hr of steam and an LTHW recovery system generating up to 569kWt.


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When installing a


CHP system, specifiers can choose between two primary power sources: gas reciprocating engines or gas turbines. Each technology has attributes that will make it more suitable for the specific conditions of fuel type and quality, electric and heat load profile, physical space, altitude, ambient conditions and other factors.


full-load operation for extended annual hours and the favourable economics of CHP can make them attractive for continuous, base-load duty. Turbines produce a large volume of exhaust at temperatures of roughly 900° F (490° C). As a result, they produce a high quality, high pressure and high volume of steam, well in excess of 100 psi (690 kPa), suited for many industrial processes. Combustion turbines also have high excess oxygen in the exhaust, enabling significant variations in thermal output.


While gas turbines have a reputation for delivering thermal efficiency, there are


key points of differentiation that often make a gas reciprocating engine more suitable for many applications. Today’s advanced lean-burn reciprocating engines are generally more fuel-efficient than turbines in pure electric power applications. They offer a lower initial cost per kW in smaller projects, typically less than 10MW, as well as being more tolerant of high altitude and higher ambient temperatures. They also operate on low-pressure fuel – 1.5 tp 5 psi (10 to 35 kPa) – eliminating the costs to install and maintain a fuel compression system. In CHP systems,


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reciprocating engines have multiple recoverable heat sources: exhaust, jacket water, aftercooler and oil cooler. They can produce heat in the forms of warm water, hot water, and low to medium-pressure steam (from exhaust).


Unlike gas turbines, gas- fuelled reciprocating engines can also be located near to the point of use, which is extremely valuable when specifiers are seeking a solution with minimal energy wastage.


Specifying the correct CHP solution can realise a range of energy efficiencies and cost saving benefits, ensuring businesses and organisations meet their strategic, financial and sustainability goals. While a CHP system might appear to be a significant cost at the outset, the benefits it can help realise means many organisations are looking to CHP as a long-term investment in the future of their business.


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